1. Field of the Invention
The present invention relates to a cooling unit adapted for use in an ice making mechanism of an auger type ice maker, a freezing mechanism of an ice cream making machine or a freezing mechanism of the other type cooling equipment.
2. Description of the Prior Art
Disclosed in Japanese Patent Laid-open Publication No. 11(1999)-132610 is a cooling unit used in a ice making mechanism of an auger type ice maker, wherein a metallic freezing pipe is helically wound around the outer periphery of a metallic cylindrical evaporator housing through a metallic filler for thermal contact with the evaporator housing. In the cooling unit, the metallic filler is embedded in a helical space between the evaporator housing and the freezing pipe to enhance the heat-exchange efficiency of the cooling unit.
It is, however, difficult to completely deposit the metallic filler into the helical space between the evaporator housing and the freezing pipe. If the metallic filler is partly chipped, an undesired space is inevitably formed between the evaporator housing and the freezing pipe. In addition, if the metallic filler causes corrosion of the evaporator housing at its embedded portion, there will occur an undesired space at the corroded portion of the evaporator housing. In such an instance, water entered into the space from the exterior is repeatedly frozen and melted in operation and stopping of the cooling unit. This results in enlargement of the undesired space between the evaporator housing and the freezing pipe and progress of the corrosion of the evaporator housing. The enlargement of undesired space in communication with the exterior deteriorates the cooling performance of the unit. If the evaporator housing is squeezed by the repetitive freeze and melting of the water, the cooling performance of the unit is further deteriorated by deformation of the evaporator housing.
It is, therefore, a primary object of the present invention to provide a cooling unit capable of overcoming the problems discussed above.
According to the present invention, there is provided a cooling unit composed of a metallic cylindrical evaporator housing and a metallic freezing pipe helically wound around the evaporator housing through a metallic filler for thermal contact with the evaporator housing, wherein the entirety of the helical freezing pipe is covered with a metallic surface layer membrane formed thereon.
In a practical embodiment of the cooling unit, the evaporator housing is made of stainless steel, the freezing pipe is made of copper, and the metallic filler is in the form of solder injected in a melted condition into a space between the evaporator housing and freezing pipe and embedded in the space in a solid condition. In this embodiment, the metallic surface layer membrane is in the form of a surface layer membrane of tin sprayed in a melted condition to the outer periphery of the freezing pipe in entirety.
In the cooling unit according to the present invention, the metallic surface layer membrane is useful to completely insulate the embedded metallic filler from the exterior. This is effective to restrain entry of the water into a space inevitably formed in the embedded portion of the metallic filler and to restrain corrosion of the metallic filler in contact with the evaporator housing. In addition, even if an undesired space in the embedded portion of the metallic filler is enlarged during a long period of time, communication of the enlarged space with the exterior is blocked by the surface layer membrane. Thus, the cooling performance of the unit is maintained in a good condition for a long period of time.
In the case that the evaporator housing is made of stainless steel, the freezing pipe is made of copper, the metallic filler is in the form of solder embedded in a space between the evaporator housing and freezing pipe and the surface layer membrane is in the form of a surface layer membrane of tin, the surface layer membrane of tin acts as a sacrifice anode to the freezing pipe, of copper to prevent leakage of refrigerant caused by corrosion of the freezing pipe.